Study On Preparation,microstructure And Properties Of Multilevel Nanostructured TiO₂

Nano-TiO₂ is widely used in the fields of environmental pollutant purification,biotechnology,energy storage and other fields due to its good biocompatibility,stability,availability and relatively low cost.The dealloying method is a simple and efficient method for preparing nanomaterials.In recent years,researchers have used the dealloying method to prepare nanometer TiO₂ with different morphologies and explore the formation mechanism,but the theory is still incomplete.The large band gap width and relatively low conductivity limit its further application.In this dissertation,the hierarchical nanostructured TiO₂ was prepared by dealloying.The effects of precursor composition,dealloying time,dealloying temperature,concentration of dealloying solution,and dealloying atmosphere on the structure and valence of nano-TiO₂ were systematically studied.The controllable preparation of simultaneous doping and oxygen deficiency was achieved.The formation mechanism of nano-TiO₂ under different conditions was discussed,and the application of nano-TiO₂ in lithium sulfur batteries and photocatalytic materials was studied.(1)The Ti₁₀Al₉₀ alloy was dealloyed in 2 mol/L Na OH solution for 72 h at 25?under the air atmosphere to prepare nanoporous TiO₂ with the pore size of about 40 nm.With the increasing of dealloying time,the porous morphology gradually penetrated from the surface of the foil to the interior.At the same time,as the dealloying temperature and solution concentration increase,the average pore size of the product gradually increases and become unevenly distributed.In addition,Ti₁₀Al₉₀alloy was dealloyed in 2 mol/L solution for 24 h under argon atmosphere,and oxygen-deficient nanoporous TiO₂(TiO_2-x)with the pore size of about 6 nm was formed.When the dealloying time is extended to 48 h,the pore size increased and oxygen defects disappear.The surface pores of the dealloyed products in the air atmosphere are coarse and unevenly distributed,and no oxygen defects are formed.(2)The Ti₃₀Cu₇₀ amorphous alloy foils were dealloyed for 48 h to obtain N-doped nanorod TiO₂with an average length of 91 nm and a diameter of about 30 nm.The band gap was 2.91 e V.With the increasing of dealloying time,the size of the nanorods and the band gap gradually increase.After 72 h of dealloying,the average length and diameter of TiO₂ are 490 and 250 nm,respectively,and the band gap is 2.98 e V.And with the increasing of dealloying time,the N content in TiO₂ gradually decreases.(3)As the cathode material for lithium-sulfur batteries,TiO_2-x/S composite have the capacity retention rate of 60.06%after 1000 cycles at the current density of 1 C,while the capacity retention rate of TiO₂/S cathode without oxygen defects is only 28.70%.At the same time,the nanoporous TiO₂/graphene oxide(GO)composite was used as the lithium-sulfur battery separator material.After 100 cycles at the current density of 0.2 C,the capacity retention rate is 76.48%,while the capacity retention rate of the lithium-sulfur battery with the original separator is only 61.65%.(4)After 48 h of dealloying,N-doped TiO₂/(Ca,Y)F₂:Yb³⁺,Tm³⁺composites were used as photocatalysts.After 10 h of near-infrared light at 980 nm,the degradation rate of methyl orange is 65.6%.With the increasing of dealloying time,the degradation rate of methyl orange by N-doped TiO₂ composites gradually decreases.When the dealloying time is 72 h,the degradation rate is 22.7%.